Organic Electroluminescence Device And Method For Producing The Same

ABSTRACT

An organic electroluminescence device including an anode, a cathode, an organic layer disposed between the anode and the cathode, the organic layer containing a hole injection layer, a hole transport layer and an emission layer containing a host material, wherein the hole injection layer, the hole transport layer and the emission layer each contain a phosphorescent light-emitting material, wherein the hole injection layer contains the phosphorescent light-emitting material in an amount of 10% by mass or more but less than 50% by mass, and wherein a concentration of the phosphorescent light-emitting material contained in the hole transport layer is lower than that in the hole injection layer, and a concentration of the phosphorescent light-emitting material contained in the emission layer is lower than that in the hole injection layer and higher than that in the hole transport layer.

TECHNICAL FIELD

The present invention relates to an organic electroluminescence deviceand a method for producing the organic electroluminescence device.

BACKGROUND ART

Organic electroluminescence devices have advantageous features such asself emission and high-speed response, and are expected for theapplication to flat panel displays. In particular, since such organicelectroluminescence devices were reported that have a dual-layerstructure (lamination type) in which a hole-transporting organic thinfilm (hole transport layer) is laminated on an electron-transportingorganic thin film (electron transport layer), organicelectroluminescence devices have been attracting attention as alarge-area light-emitting device that emits light at a low voltage of 10V or lower. The organic electroluminescence devices of lamination typehave a basic structure of anode/hole transport layer/emissionlayer/electron transport layer/cathode.

Various attempts have been made to elongate the service life of suchorganic electroluminescence devices. For example, PTL 1 and otherliteratures disclose an organic electroluminescence device including anemission layer containing a host material in an amount of 50% by mass ormore and a hole transport layer containing the host material in anamount of 5% by mass to 50% by mass or more, wherein the emission layercontains substantially no material other than the host material amongthe hole transporting materials contained in the hole transport layer.

Also, PTL 2 and other literatures disclose an organicelectroluminescence device including a hole injection layer, a holetransport layer and an emission layer each containing a phosphorescentlight-emitting material, wherein the hole injection layer contains thephosphorescent light-emitting material in an amount of 10% by mass to90% by mass and wherein the concentration of the phosphorescentlight-emitting material contained in the hole transport layer is lowerthan that in the hole injection layer and higher than that in theemission layer.

In addition, PTL 3 and other literatures disclose an organicelectroluminescence device including a hole injection layer, a holetransport layer, an emission layer and a mixture layer, wherein themixture layer is disposed between the emission layer and the holeinjection layer or the hole transport layer.

However, these organic electroluminescence devices cannot attain highexternal quantum efficiency although their service life is elongated.

In view of this, keen demand has arisen for development of an organicelectroluminescence device exhibiting high external quantum efficiencyand a method for producing the organic electroluminescence device.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Application Laid-Open (JP-A) No. 2008-78373

PTL 2: International Publication No. WO09/030981

PTL 3: JP-A No. 2007-242910

SUMMARY OF INVENTION Technical Problem

The present invention solves the above existing problems and aims toachieve the following object. Specifically, an object of the presentinvention is to provide an organic electroluminescence device havinghigh external quantum efficiency and a method for producing the organicelectroluminescence device.

Solution to Problem

Means for solving the above existing problems are as follows.

<1> An organic electroluminescence device including:

an anode,

a cathode,

an organic layer disposed between the anode and the cathode,

the organic layer containing a hole injection layer, a hole transportlayer and an emission layer containing a host material,

wherein the hole injection layer, the hole transport layer and theemission layer each contain a phosphorescent light-emitting material,

wherein the hole injection layer contains the phosphorescentlight-emitting material in an amount of 10% by mass or more but lessthan 50% by mass, and

wherein a concentration of the phosphorescent light-emitting materialcontained in the hole transport layer is lower than that in the holeinjection layer, and a concentration of the phosphorescentlight-emitting material contained in the emission layer is lower thanthat in the hole injection layer and higher than that in the holetransport layer.

<2> The organic electroluminescence device according to <1>, wherein thehole transport layer further contains the host material.

<3> The organic electroluminescence device according to <2>, wherein aratio by mass of the phosphorescent light-emitting material to the hostmaterial in the emission layer is one to ten times a ratio by mass ofthe phosphorescent light-emitting material to the host material in thehole transport layer.

<4> The organic electroluminescence device according to any one of <1>to <3>, wherein the concentration of the phosphorescent light-emittingmaterial contained in the hole transport layer is changed from aninterface between the hole transport layer and the emission layer to aninterface between the hole transport layer and the hole injection layer.

<5> The organic electroluminescence device according to any one of <2>to <4>, wherein the concentration of the host material contained in thehole transport layer is changed from an interface between the holetransport layer and the emission layer to an interface between the holetransport layer and the hole injection layer.

<6> The organic electroluminescence device according to any one of <1>to <5>, wherein the phosphorescent light-emitting material has anasymmetric structure.

<7> The organic electroluminescence device according to any one of <1>to <6>, wherein the phosphorescent light-emitting material is a compoundrepresented by General Formula (1) below:

(L1)₂-Ir-(L2)₁  General Formula (1)

where L1 denotes a ligand and L2 denotes a ligand different from L1.

<8> The organic electroluminescence device according to any one of <1>to <7>, wherein the host material is a compound represented by GeneralFormula (2) below:

where R represents a t-butyl group, a t-amyl group, a trimethylsilylgroup, a triphenylsilyl group or a phenyl group, and R₁ to R₂₃ eachrepresent a hydrogen atom, a C₁-C₅ alkyl group, a cyano group, afluorine atom, a trifluoro group, a trimethylsilyl group, atriphenylsilyl group or a phenyl group.

<9> The organic electroluminescence device according to any one of <1>to <8>, wherein the hole injection layer further contains an arylaminederivative and an ionization potential of the arylamine derivative is4.8 eV to 5.8 eV and wherein a difference between the ionizationpotential of the arylamine derivative and an ionization potential of thephosphorescent light-emitting material contained in the hole injectionlayer is within ±0.2 eV.

<10> An organic electroluminescence device-producing method forproducing the organic electroluminescence device according to any one of<1> to <9>, including:

forming the hole injection layer, the hole transport layer and theemission layer through coating.

<11> The organic electroluminescence device-producing method accordingto <10>, wherein the phosphorescent light-emitting material is solubleto a solvent used for the coating.

Advantageous Effects of Invention

The present invention can provide an organic electroluminescence deviceexhibiting high external quantum efficiency and a method for producingthe organic electroluminescence device. These can solve the aboveexisting problems and achieve the above object.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the concentration of a phosphorescentlight-emitting material contained in a hole injection layer, a holetransport layer and an emission layer of an organic electroluminescencedevice of the present invention (part 1).

FIG. 2 is a graph showing the concentration of a phosphorescentlight-emitting material contained in a hole injection layer, a holetransport layer and an emission layer of an organic electroluminescencedevice of the present invention (part 2).

FIG. 3 is a graph showing the concentration of a host material containedin a hole injection layer, a hole transport layer and an emission layerof an organic electroluminescence device of the present invention (part1).

FIG. 4 is a graph showing the concentration of a host material containedin a hole injection layer, a hole transport layer and an emission layerof an organic electroluminescence device of the present invention (part2).

FIG. 5 is a schematic view of one exemplary layer structure of anorganic electroluminescence device of the present invention.

FIG. 6 is a graph showing the Ir concentration (profile of filmthickness) contained in a hole injection layer, a hole transport layerand an emission layer of an organic electroluminescence device ofExample 3.

DESCRIPTION OF EMBODIMENTS (Organic Electroluminescence Device)

An organic electroluminescence device of the present invention includesa pair of electrodes (anode and cathode) and an organic layer disposedbetween the electrodes; and, if necessary, further includes otherlayers.

<Organic Layer>

The organic layer includes at least a hole injection layer, a holetransport layer and an emission layer; and, if necessary, furtherincludes other layers.

<<Hole Injection Layer and Hole Transport Layer>>

The hole injection layer and hole transport layer are layers having thefunction of receiving holes from the anode or from the anode side andtransporting the holes to the cathode side. Each of the hole injectionlayer and the hole transport layer may have a single-layered structureor a multi-layered structure made of a plurality of layers which areidentical or different in composition.

The hole injection layer and the hole transport layer each contain aphosphorescent light-emitting material.

The amount of the phosphorescent light-emitting material contained inthe hole injection layer is not particularly limited, so long as it is10% by mass or more but less than 50% by mass, and may be appropriatelyselected depending on the intended purpose. The amount thereof ispreferably 20% by mass to 45% by mass, more preferably 20% by mass to40% by mass, particularly preferably 25% by mass to 40% by mass.

When the amount of the phosphorescent light-emitting material containedin the hole injection layer is less than 10% by mass, the concentrationby volume of the phosphorescent light-emitting material may be low. Whenthe amount thereof is 50% by mass or higher, the hole injection layermay be peeled off or dissolved when the hole transport layer is formedon the hole injection layer. When the amount of the phosphorescentlight-emitting material contained in the hole injection layer fallswithin the above particularly preferable range, the hole transport layercan be laminated on the hole injection layer through wet coating, andalso, EL efficiency is advantageously increased by the addition of thephosphorescent light-emitting material.

The concentration of the phosphorescent light-emitting materialcontained in the hole transport layer (HTL) is not particularly limited,so long as it is lower than that in the hole injection layer (HIL) asshown in, for example, FIG. 1, and may be appropriately selecteddepending on the intended purpose. The concentration thereof ispreferably changed from an interface between the hole transport layerand the emission layer (EML) to an interface between the hole transportlayer and the hole injection layer. The manner in which theconcentration thereof is changed is not particularly limited and may beappropriately selected depending on the intended purpose. For example,the concentration thereof is preferably successively (gradually) changedas shown in FIG. 2. Notably, the above-described hole transport layer(in which the concentration of the phosphorescent light-emittingmaterial is successively (gradually) changed form the interface betweenthe hole transport layer and the emission layer to the interface betweenthe hole transport layer and the hole injection layer) can be formed asa result that the phosphorescent light-emitting material contained inthe emission layer formed through coating is transferred (diffused) intothe hole transport layer.

—Phosphorescent Light-Emitting Material—

In general, examples of the phosphorescent light-emitting materialinclude complexes containing a transition metal atom or a lanthanoidatom. The phosphorescent light-emitting material preferably has anasymmetric structure.

The transition metal atom is not particularly limited and may beselected depending on the intended purpose. Preferred are ruthenium,rhodium, palladium, tungsten, rhenium, osmium, iridium and platinum.More preferred are rhenium, iridium and platinum. Particularly preferredare iridium and platinum.

The lanthanoid atom is not particularly limited and may be appropriatelyselected depending on the intended purpose. Examples thereof includelanthanum, cerium, praseodymium, neodymium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium andlutetium, with neodymium, europium and gadolinium being preferred.

The ligand in the complexes is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include those described in, for example, “ComprehensiveCoordination Chemistry” authored by G. Wilkinson et al., published byPergamon Press Company in 1987; “Photochemistry and Photophysics ofCoordination Compounds” authored by H. Yersin, published bySpringer-Verlag Company in 1987; and “YUHKIKINZOKUKAGAKU-KISO TOOUYOU—(Metalorganic Chemistry—Fundamental and Application—)” authored byAkio Yamamoto, published by Shokabo Publishing Co., Ltd. in 1982.

The ligand is not particularly limited and may be appropriately selecteddepending on the intended purpose. Preferred are halogen ligands,preferably, chlorine ligand aromatic carbon ring ligands such ascyclopentadienyl anion, benzene anion and naphthyl anion;nitrogen-containing hetero cyclic ligands such as phenyl pyridine,benzoquinoline, quinolinol, bipyridyl and phenanthrorine); diketoneligands such as acetyl acetone; carboxylic acid ligands such as aceticacid ligand); alcoholate ligands such as phenolate ligand; carbonmonoxide ligand; isonitrile ligand; and cyano ligand, withnitrogen-containing hetero cyclic ligands being more preferred.

The above-described complexes may be a complex containing one transitionmetal atom in the compound, or a so-called polynuclear complexcontaining two or more transition metal atoms. In the latter case, thecomplexes may contain different metal atoms at the same time. Examplesof the phosphorescent light-emitting material include Ir complexes andPt complexes. The Ir complexes are preferably those represented by thefollowing General Formula (1). Also, specific examples of the Ircomplexes and Pt complexes include the following Ir complexes and Ptcomplexes, but employable phosphorescent light-emitting materials arenot construed as being limited thereto.

Of these, particularly preferred are compounds having asymmetricstructures expressed by Structural Formulas (2), (3) and (7), since theyare soluble to a solvent used for the formation, through coating, of thehole injection layer, the hole transport layer and the emission layer.The asymmetric structure refers to a structure in which at least one ofthe ligands coordinating with the central metal is different from theother ligands like the compounds having Structural Formulas (2), (3) and(7). Furthermore, like the compounds having Structural Formulas (3) and(7), complexes which have asymmetric structures and whose ligands arecoordinated via only C and N are more preferred, since they exhibit highthermodecomposition temperature.

The solvent is not particularly limited and may be appropriatelyselected depending on the intended purpose. Examples thereof includecyclohexanone, tetrahydrofuran, toluene, xylene and 2-butanone.

The drying temperature is a temperature higher than the boiling point ofthe solvent, more preferably a temperature higher by 10° C. than theboiling temperature of the solvent. The drying time is several minutesto several hours, more preferably 2 min to 120 min. Notably, vacuumdrying, an inert oven (inert gas atmosphere), etc. may be appropriatelyemployed.

The hole transport layer (HTL) is not particularly limited, so long asit contains the phosphorescent light-emitting material, and may beappropriately selected depending on the intended purpose. Preferably,the hole transport layer contains the host material as shown in FIG. 3,for example.

The concentration of the host material contained in the hole transportlayer (HTL) is preferably changed from the interface between aninterface between the hole transport layer (HTL) and the emission layer(EML) to an interface between the hole transport layer (HTL) and thehole injection layer (HIL). The manner in which the concentrationthereof is changed is not particularly limited and may be appropriatelyselected depending on the intended purpose. For example, theconcentration thereof is preferably successively (gradually) changed asshown in FIG. 4. Notably, the above-described hole transport layer (inwhich the concentration of the host material is successively (gradually)changed form the interface between the hole transport layer and theemission layer to the interface between the hole transport layer and thehole injection layer) can be formed as a result that the host materialcontained in the emission layer formed through coating is transferred(diffused) into the hole transport layer.

—Host Material—

The host material is not particularly limited and may be appropriatelyselected depending on the intended purpose. Examples thereof includehole transporting hosts such as compounds represented by the followingGeneral Formulas (2) and (3).

where R represents a t-butyl group, a t-amyl group, a trimethylsilylgroup, a triphenylsilyl group or a phenyl group, and R₁ to R₂₃ eachrepresent a hydrogen atom, a C₁-C₅ alkyl group, a cyano group, afluorine atom, a trifluoro group, a trimethylsilyl group, atriphenylsilyl group or a phenyl group.

where R represents a t-butyl group, a t-amyl group, a trimethylsilylgroup, a triphenylsilyl group or a phenyl group, and R₁ to R₂₃ eachrepresent a hydrogen atom, a C₁-C₅ alkyl group, a cyano group, afluorine atom, a trifluoro group, a trimethylsilyl group, atriphenylsilyl group or a phenyl group.

The hole transporting host materials represented by General Formula (2)are not particularly limited and may be appropriately selected dependingon the intended purpose. Examples thereof include the followingcompounds.

The hole transporting host materials represented by General Formula (3)are not particularly limited and may be appropriately selected dependingon the intended purpose. Examples thereof include the followingcompounds.

—Hole Transporting Host Material—

The ionization potential Ip of the hole transporting host material isnot particularly limited and may be appropriately selected depending onthe intended purpose. The ionization potential Ip thereof is preferably5.1 eV to 6.4 eV, more preferably 5.4 eV to 6.2 eV, particularlypreferably 5.6 eV to 6.0 eV, from the viewpoints of improvement indurability and decrease in drive voltage.

The electron affinity Ea of the hole transporting host material is notparticularly limited and may be appropriately selected depending on theintended purpose. The electron affinity Ea thereof is preferably 1.2 eVto 3.1 eV, more preferably 1.4 eV to 3.0 eV, particularly preferably 1.8eV to 2.8 eV, from the viewpoints of improvement in durability anddecrease in drive voltage.

The lowest triplet excitation energy (hereinafter may be referred to as“T1”) of the hole transporting host material is not particularly limitedand may be appropriately selected depending on the intended purpose. Thelowest triplet excitation energy thereof is preferably 2.2 eV to 3.7 eV,more preferably 2.4 eV to 3.7 eV, particularly preferably 2.4 eV to 3.4eV.

The hole transporting host material is not particularly limited and maybe appropriately selected depending on the intended purpose. Examples ofthe hole transporting host material include pyrrole, indole, carbazole,azaindole, azacarbazole, pyrazole, imidazole, polyarylalkane,pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substitutedchalcone, styrylanthracene, fluorenone, hydrazone, stilbene, silazane,aromatic tertiary amine compounds, styrylamine compounds, aromaticdimethylidine compounds, porphyrin compounds, polysilane compounds,poly(N-vinylcarbazole), aniline copolymers, conductivehigh-molecular-weight oligomers (e.g., thiophene oligomers andpolythiophenes), organic silanes, carbon films and derivatives thereof.

Among them, preferred are indole derivatives, carbazole derivatives,azaindole derivatives, azacarbazole derivatives, aromatic tertiary aminecompounds and thiophene derivatives. Particularly preferred arecompounds having, in their molecule, a plurality of indole skeletons,carbazole skeletons, azaindole skeletons, azacarbazole skeletons oraromatic tertiary amine skeletons.

Also, in the present invention, host materials part or all of thehydrogen atoms of which have been substituted by deuterium may be used(JP-A Nos. 2009-277790 and 2004-515506).

—Hole Injection Material and Hole Transport Material—

Other hole injection materials or hole transport materials used in thehole injection layer or the hole transport layer are not particularlylimited and may be appropriately selected depending on the intendedpurpose. They may be, for example, low-molecular-weight compounds andhigh-molecular-weight compounds.

The hole injection materials or the hole transport materials are notparticularly limited and may be appropriately selected depending on theintended purpose. Examples thereof include pyrrole derivatives,carbazole derivatives, triazole derivatives, oxazole derivatives,oxadiazole derivatives, imidazole derivatives, polyarylalkanederivatives, pyrazoline derivatives, pyrazolone derivatives,phenylenediamine derivatives, arylamine derivatives, amino-substitutedchalcone derivatives, styrylanthracene derivatives, fluorenonederivatives, hydrazone derivatives, stilbene derivatives, silazanederivatives, aromatic tertiary amine compounds, styrylamine compounds,aromatic dimethylidine compounds, phthalocyanine compounds, porphyrincompounds, thiophene derivatives, organosilane derivatives and carbon.These may be use alone or in combination.

In particular, the material for the hole injection layer is preferablyhigh-molecular-weight compounds for the following reasons: (1) highadhesion to the electrode can be obtained to prevent delaminationoccurring at the interface between the electrode and the organic layer(the hole injection layer) when driving EL and (2) the resultantsolution is thickened to prevent aggregation of the phosphorescentlight-emitting material.

Of these, arylamine derivatives are preferred. More preferred arecompounds having the following Structural Formulas (4) and (5)(Mw=8,000, on the basis of standard polystyrene), PTPDES-2 and PTPDES(these products are of CHEMIPRO KASEI KAISHA, LTD.), a compound havingthe following Structural Formula (8) (HTL-1 described in U.S. Pat. No.2008/0220265). The weight average molecular weight of the compoundhaving Structural Formula (4) was calculated through gel permeationchromatography or GPC on the basis of standard polystyrene.

Notably, to prevent excessive mixing between the layers, the layers mayhave crosslinked portions. The crosslinking method may be any methodsuch as sol-gel crosslinking, radical polymerization, cationpolymerization or ring-opening polymerization.

where n is an integer of 1 or greater.

where n is an integer of 1 or greater.

The ionization potential of the arylamine derivative contained in thehole injection layer is not particularly limited and may beappropriately selected depending on the intended purpose. The ionizationpotential thereof is preferably 4.8 eV to 5.8 eV, more preferably 5.2 eVto 5.8 eV, particularly preferably 5.4 eV to 5.8 eV. When the ionizationpotential of the arylamine derivative is lower than 4.8 eV and hencelower than that of an ITO electrode, the hole injection barrier to theadjacent hole transport layer may be large. Whereas when the ionizationpotential of the arylamine derivative is higher than 5.8 eV, theinjection barrier to the ITO electrode may be large. When the ionizationpotential of the arylamine derivative falls within the aboveparticularly preferable range, the injection barrier from the ITO to thehole injection layer becomes small and the injection barrier from thehole injection layer to the hole transport layer becomes also small,which is advantageous in terms of reduction of driving voltage oforganic electroluminescence devices.

The difference between the ionization potential of the arylaminederivative contained in the hole injection layer and the ionizationpotential of the phosphorescent light-emitting material contained in thehole injection layer is not particularly limited and may beappropriately selected depending on the intended purpose. The differencetherebetween is preferably within ±0.2 eV. In this case, holes areinjected into both the arylamine derivative and the phosphorescentlight-emitting material and hence the hole injection layer is improvedin conductivity, which is advantageous in terms of improvement in powerefficiency of organic electroluminescence devices.

The hole injection layer or the hole transport layer may contain anelectron-accepting dopant.

The electron-accepting dopant is not particularly limited and may beappropriately selected depending on the intended purpose. Theelectron-accepting dopant may be, for example, an inorganic or organiccompound, so long as it has electron accepting property and the functionof oxidizing an organic compound.

The inorganic compound is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include metal halides (e.g., ferric chloride, aluminum chloride,gallium chloride, indium chloride and antimony pentachloride) and metaloxides (e.g., vanadium pentaoxide and molybdenum trioxide).

The organic compound is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include compounds having a substituent such as a nitro group, ahalogen, a cyano group and a trifluoromethyl group; quinone compounds;acid anhydride compounds; and fullerenes.

These electron-accepting dopants may be used alone or in combination.

The amount of the electron-accepting dopant used varies depending on thetype of the material. The amount thereof is preferably 0.01% by mass to50% by mass, more preferably 0.05% by mass to 20% by mass, particularlypreferably 0.1% by mass to 10% by mass, relative to the hole transportmaterial or the hole injection material.

The thickness of the hole injection layer or the hole transport layer isnot particularly limited and may be appropriately selected depending onthe intended purpose. The thickness thereof is preferably 1 nm to 500nm, more preferably 5 nm to 200 nm, particularly preferably 10 nm to 100nm.

<<Emission Layer>>

The emission layer is a layer having the functions of receiving holesfrom the anode, the hole injection layer, or the hole transport layer,and receiving electrons from the cathode, the electron injection layer,or the electron transport layer, and providing a field for recombinationof the holes with the electrons for light emission, when an electricfield is applied.

The emission layer contains the phosphorescent light-emitting material.The concentration of the phosphorescent light-emitting materialcontained in the emission layer is lower than that in the hole injectionlayer and higher than that in the hole transport layer.

The phosphorescent light-emitting material is not particularly limitedand may be appropriately selected depending on the intended purpose. Thephosphorescent light-emitting material may be, for example, those usedin the hole injection layer and the hole transport layer.

The emission layer contains a host material.

The host material is not particularly limited and may be appropriatelyselected depending on the intended purpose. The host material may be,for example, the hole transporting hosts used in the hole transportlayer and the below-described electron transporting host materials.

The ratio by mass of the phosphorescent light-emitting material to thehost material in the emission layer (the mass of the phosphorescentlight-emitting material/the mass of the host material) is notparticularly limited and may be appropriately selected depending on theintended purpose. The ratio by mass of the phosphorescent light-emittingmaterial to the host material in the emission layer is preferably one toten times, more preferably one to five times the ratio by mass of thephosphorescent light-emitting material to the host material in the holetransport layer (the mass of the phosphorescent light-emittingmaterial/the mass of the host material). When the ratio by mass of thephosphorescent light-emitting material to the host material in theemission layer is less than one time the ratio by mass of thephosphorescent light-emitting material to the host material in the holetransport layer, the hole mobility may be decreased. When the ratio bymass of the phosphorescent light-emitting material to the host materialin the emission layer is more than ten times the ratio by mass of thephosphorescent light-emitting material to the host material in the holetransport layer, an excessive amount of holes are injected into theemission layer to accelerate degradation of the adjacent layers,especially the electron transport layer, resulting in that thedurability of the organic electroluminescence device may be decreased.When the ratio by mass of the phosphorescent light-emitting material tothe host material in the emission layer falls within the aboveparticularly preferable range, the resultant organic electroluminescencedevice is advantageously improved in power efficiency and durability.

The thickness of the emission layer is not particularly limited and maybe appropriately selected depending on the intended purpose. Thethickness thereof is preferably 2 nm to 500 nm. From the viewpoint ofincreasing the external quantum efficiency, the thickness thereof ismore preferably 3 nm to 200 nm, particularly preferably 10 nm to 200 nm.The organic emission layer may be a single layer or two or more layers.When it is two or more layers, the layers may emit lights of differentcolors.

—Electron Transporting Host Material—

The electron affinity Ea of the electron transporting host material isnot particularly limited and may be appropriately selected depending onthe intended purpose. The electron affinity Ea thereof is preferably 2.5eV to 3.5 eV, more preferably 2.6 eV to 3.4 eV, further preferably 2.8eV to 3.3 eV, from the viewpoints of improvement in durability anddecrease in drive voltage.

The ionization potential Ip of the electron transporting host materialis not particularly limited and may be appropriately selected dependingon the intended purpose. The ionization potential Ip thereof ispreferably 5.7 eV to 7.5 eV, more preferably 5.8 eV to 7.0 eV, furtherpreferably 5.9 eV to 6.5 eV, from the viewpoints of improvement indurability and decrease in drive voltage.

The lowest triplet excitation energy (hereinafter may be referred to as“T1”) of the electron transporting host material is not particularlylimited and may be appropriately selected depending on the intendedpurpose. The lowest triplet excitation energy thereof is preferably 2.2eV to 3.7 eV, more preferably 2.4 eV to 3.7 eV, particularly preferably2.4 eV to 3.4 eV.

The electron transporting host material is not particularly limited andmay be appropriately selected depending on the intended purpose.Examples thereof include pyridine, pyrimidine, triazine, imidazole,pyrazole, triazole, oxazole, oxadiazole, fluorenone,anthraquinonedimethane, anthrone, diphenylquinone, thiopyrandioxide,carbodiimide, fluorenylidenemethane, distyrylpyradine,fluorine-substituted aromatic compounds, heterocyclic tetracarboxylicanhydrides (e.g., naphthalene and perylene), phthalocyanine, derivativesthereof (which may form a condensed ring with another ring) and variousmetal complexes such as metal complexes of 8-quinolynol derivatives,metal phthalocyanine, and metal complexes having benzoxazole orbenzothiazole as a ligand.

The electron transporting host is not particularly limited and may beappropriately selected depending on the intended purpose. Preferred aremetal complexes, azole derivatives (e.g., benzimidazole derivatives andimidazopyridine derivatives) and azine derivatives (e.g., pyridinederivatives, pyrimidine derivatives and triazine derivatives). Amongthem, metal complexes are more preferred in terms of durability.

The metal complex is not particularly limited and may be appropriatelyselected depending on the intended purpose. Preferred are metalcomplexes containing a ligand which has at least one nitrogen atom,oxygen atom, or sulfur atom and which is coordinated with the metal.

The metal ion contained in the metal complex is not particularly limitedand may be appropriately selected depending on the intended purpose. Itis preferably a beryllium ion, a magnesium ion, an aluminum ion, agallium ion, a zinc ion, an indium ion, a tin ion, a platinum ion or apalladium ion; more preferably a beryllium ion, an aluminum ion, agallium ion, a zinc ion, a platinum ion or a palladium ion; particularlypreferably an aluminum ion, a zinc ion, a platinum ion or a palladiumion.

The ligand contained in the metal complexes is not particularly limitedand may be appropriately selected depending on the intended purpose.Although there are a variety of known ligands, examples thereof includethose described in, for example, “Photochemistry and Photophysics ofCoordination Compounds” authored by H. Yersin, published bySpringer-Verlag Company in 1987; and “YUHKIKINZOKUKAGAKU-KISO TOOUYOU—(Metalorganic Chemistry—Fundamental and Application—)” authored byAkio Yamamoto, published by Shokabo Publishing Co., Ltd. in 1982.

The ligand is not particularly limited and may be appropriately selecteddepending on the intended purpose. The ligand is preferablynitrogen-containing heterocyclic ligands (preferably having 1 to 30carbon atoms, more preferably 2 to 20 carbon atoms, particularlypreferably 3 to 15 carbon atoms). It may be a unidentate ligand or a bi-or higher-dentate ligand.

The ligand is not particularly limited and may be appropriately selecteddepending on the intended purpose. Preferred are bi- to hexa-dentateligands, and mixed ligands of bi- to hexa-dentate ligands with aunidentate ligand.

The ligand is not particularly limited and may be appropriately selecteddepending on the intended purpose. Examples of the ligand include azineligands (e.g., pyridine ligands, bipyridyl ligands and terpyridineligands); hydroxyphenylazole ligands (e.g., hydroxyphenylbenzoimidazoleligands, hydroxyphenylbenzoxazole ligands, hydroxyphenylimidazoleligands and hydroxyphenylimidazopyridine ligands); alkoxy ligands (thosehaving preferably 1 to 30 carbon atoms, more preferably 1 to 20 carbonatoms, particularly preferably 1 to 10 carbon atoms, such as methoxy,ethoxy, butoxy and 2-ethylhexyloxy); and aryloxy ligands (those havingpreferably 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms,particularly preferably 6 to 12 carbon atoms, such as phenyloxy,1-naphthyloxy, 2-naphthyloxy, 2,4,6-trimethylphenyloxy and4-biphenyloxy), heteroaryloxy ligands (those having preferably 1 to 30carbon atoms, more preferably 1 to 20 carbon atoms, particularlypreferably 1 to 12 carbon atoms, examples of which include pyridyloxy,pyrazyloxy, pyrimidyloxy and quinolyloxy); alkylthio ligands (thosehaving preferably 1 to 30 carbon atoms, more preferably 1 to 20 carbonatoms, particularly preferably 1 to 12 carbon atoms, examples of whichinclude methylthio and ethylthio); arylthio ligands (those havingpreferably 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms,particularly preferably 6 to 12 carbon atoms, examples of which includephenylthio); heteroarylthio ligands (those having preferably 1 to 30carbon atoms, more preferably 1 to 20 carbon atoms, particularlypreferably 1 to 12 carbon atoms, examples of which include pyridylthio,2-benzimidazolylthio, 2-benzoxazolylthio and 2-benzothiazolylthio);siloxy ligands (those having preferably 1 to 30 carbon atoms, morepreferably 3 to 25 carbon atoms, particularly preferably 6 to 20 carbonatoms, examples of which include a triphenylsiloxy group, atriethoxysiloxy group and a triisopropylsiloxy group); aromatichydrocarbon anion ligands (those having preferably 6 to 30 carbon atoms,more preferably 6 to 25 carbon atoms, particularly preferably 6 to 20carbon atoms, examples of which include a phenyl anion, a naphthyl anionand an anthranyl anion); aromatic heterocyclic anion ligands (thosehaving preferably 1 to 30 carbon atoms, more preferably 2 to 25 carbonatoms, and particularly preferably 2 to 20 carbon atoms, examples ofwhich include a pyrrole anion, a pyrazole anion, a triazole anion, anoxazole anion, a benzoxazole anion, a thiazole anion, a benzothiazoleanion, a thiophene anion and a benzothiophene anion); and indolenineanion ligands.

Among them, nitrogen-containing heterocyclic ligands, aryloxy ligands,heteroaryloxy groups, siloxy ligands, etc. are more preferred, andnitrogen-containing heterocyclic ligands, aryloxy ligands, siloxyligands, aromatic hydrocarbon anion ligands, aromatic heterocyclic anionligands, etc. are particularly preferred.

The metal complexes used for the electron transporting host material arecompounds described in, for example, JP-A Nos. 2002-235076, 2004-214179,2004-221062, 2004-221065, 2004-221068 and 2004-327313.

<<Other Layers>>

The other layers are not particularly limited and may be appropriatelyselected depending on the intended purpose. Examples thereof include anelectron transport layer, an electron injection layer, a hole blockinglayer and an electron blocking layer.

—Electron Transport Layer and Electron Injection Layer—

The electron injection layer or the electron transport layer is a layerhaving the function of receiving electrons from the cathode or from thecathode side and transporting the electrons to the anode side.

The thickness of the electron injection layer or the electron transportlayer is not particularly limited and may be appropriately selecteddepending on the intended purpose. The thickness thereof is preferably0.5 nm to 500 nm, more preferably 1 nm to 200 nm.

The electron injection layer or the electron transport layer is notparticularly limited and may be appropriately selected depending on theintended purpose. The electron injection layer or the electron transportlayer preferably contains a reducing dopant.

The reducing dopant is not particularly limited and may be appropriatelyselected depending on the intended purpose. The reducing dopant ispreferably at least one selected from alkali metals, alkaline-earthmetals, rare-earth metals, alkali metal oxides, alkali metal halides,alkaline-earth metal oxides, alkaline-earth metal halides, rare-earthmetal oxides, rare-earth metal halides, alkali metal organic complexes,alkaline-earth metal organic complexes and rare-earth metal organiccomplexes.

The amount of the reducing dopant used varies depending on the type ofthe material. The amount thereof is preferably 0.1% by mass to 99% bymass, more preferably 0.3% by mass to 80% by mass, particularlypreferably 0.5% by mass to 50% by mass, relative to the electrontransport material or the electron injection material.

The electron transport layer and the electron injection layer are notparticularly limited and can be formed by a known method. Specifically,suitably employed methods include a deposition method, a wet filmforming method, a molecular beam epitaxial or MBE method, a cluster ionbeam method, a molecule deposition method, an LB method, a coatingmethod and a printing method.

The thickness of the electron transport layer is not particularlylimited and may be appropriately selected depending on the intendedpurpose. The thickness thereof is preferably 1 nm to 200 nm, morepreferably 1 nm to 100 nm, particularly preferably 1 nm to 50 nm.

The thickness of the electron injection layer is not particularlylimited and may be appropriately selected depending on the intendedpurpose. The thickness thereof is preferably 1 nm to 200 nm, morepreferably 1 nm to 100 nm, particularly preferably 1 nm to 50 nm.

—Hole Blocking Layer and Electron Blocking Layer—

The hole blocking layer is a layer having the function of preventing theholes, which have been transported from the anode side to the emissionlayer, from passing toward the cathode side, and is generally providedas an organic compound layer adjacent to the emission layer on thecathode side.

The electron blocking layer is a layer having the function of preventingthe electrons, which have been transported from the cathode side to theemission layer, from passing toward the anode side, and is generallyprovided as an organic compound layer adjacent to the emission layer onthe anode side.

The compound for the hole blocking layer is not particularly limited andmay be appropriately selected depending on the intended purpose.Examples thereof include aluminum complexes (e.g., BAlq), triazolederivatives and phenanthroline derivatives (e.g., BCP).

The compound for the electron blocking layer is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples of the compound employable include the above-described holetransport materials.

The electron blocking layer and the hole blocking layer are notparticularly limited and can be formed by a known method. Specifically,suitably employed methods include a dry film forming method such as asputtering method or a deposition method, a wet coating method, atransfer method, a printing method and an inkjet method.

The thickness of the hole blocking layer or the electron blocking layeris not particularly limited and may be appropriately selected dependingon the intended purpose. The thickness thereof is preferably 1 nm to 200nm, more preferably 1 nm to 50 nm, particularly preferably 3 nm to 10nm. The hole blocking layer or the electron blocking layer may have asingle-layered structure made of one or more of the above-mentionedmaterials, or a multi-layered structure made of a plurality of layerswhich are identical or different in composition.

<Electrode>

The organic electroluminescence device of the present invention includesa pair of electrodes; i.e., an anode and a cathode. In terms of thefunction of the organic electroluminescence device, at least one of theanode and the cathode is preferably transparent. In general, the anodemay be any material, so long as it has the function of serving as anelectrode which supplies holes to the organic compound layer.

The shape, structure, size, etc. thereof are not particularly limitedand may be appropriately selected from known electrode materialsdepending on the intended application/purpose of the organicelectroluminescence device.

The material for the electrodes is not particularly limited and may beappropriately selected depending on the intended purpose. Preferredexamples of the material include metals, alloys, metal oxides,conductive compounds and mixtures thereof.

<<Anode>>

The material for the anode is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include conductive metal oxides such as tin oxides doped with,for example, antimony and fluorine (ATO and FTO), tin oxide, zinc oxide,indium oxide, indium tin oxide (ITO) and indium zinc oxide (IZO); metalssuch as gold, silver, chromium and nickel; mixtures or laminates ofthese metals and the conductive metal oxides; inorganic conductivematerials such as copper iodide and copper sulfide; organic conductivematerials such as polyaniline, polythiophene and polypyrrole; andlaminates of these materials and ITO. Among them, conductive metaloxides are preferred. In particular, ITO is preferred from theviewpoints of productivity, high conductivity, transparency, etc.

<<Cathode>>

The material for the cathode is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include alkali metals (e.g., Li, Na, K and Cs), alkaline earthmetals (e.g., Mg and Ca), gold, silver, lead, aluminum, sodium-potassiumalloys, lithium-aluminum alloys, magnesium-silver alloys and rare earthmetals (e.g., indium and ytterbium). These may be used alone, but it ispreferred that two or more of them are used in combination from theviewpoint of satisfying both stability and electron-injection property.

Among them, as the materials for forming the cathode, alkali metals oralkaline earth metals are preferred in terms of excellentelectron-injection property, and materials containing aluminum as amajor component are preferred in terms of excellent storage stability.

The term “material containing aluminum as a major component” refers to amaterial composed of aluminum alone; alloys containing aluminum and0.01% by mass to 10% by mass of an alkali or alkaline earth metal; orthe mixtures thereof (e.g., lithium-aluminum alloys andmagnesium-aluminum alloys).

The method for forming the electrodes is not particularly limited andmay be a known method. Examples thereof include wet methods such asprinting methods and coating methods; physical methods such as vacuumdeposition methods, sputtering methods and ion plating methods; andchemical methods such as CVD and plasma CVD methods. The electrodes canbe formed on a substrate by a method appropriately selected from theabove methods in consideration of their suitability to the material forthe electrodes. For example, when ITO is used as the material for theanode, the anode may be formed in accordance with a DC or high-frequencysputtering method, a vacuum deposition method, or an ion plating method.For example, when a metal (or metals) is (are) selected as the material(or materials) for the cathode, one or more of them may be appliedsimultaneously or sequentially by, for example, a sputtering method.

Patterning for forming the electrodes may be performed by a chemicaletching method such as photolithography; a physical etching method suchas etching by laser; a method of vacuum deposition or sputtering using amask; a lift-off method; or a printing method.

<Substrate>

The organic electroluminescence device of the present invention ispreferably formed on a substrate. It may be formed so that a substratecomes into direct contact with the electrodes, or may be formed on asubstrate by the mediation of an intermediate layer.

The material for the substrate is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include inorganic materials such as yttria-stabilized zirconia(YSZ) and glass (alkali-free glass and soda-lime glass); and organicmaterials such as polyesters (e.g., polyethylene terephthalate,polybutylene phthalate and polyethylene naphthalate), polystyrene,polycarbonate, polyether sulfone, polyarylate, polyimide,polycycloolefin, norbornene resins and poly(chlorotrifluoroethylene).

The shape, structure, size, etc. of the substrate are not particularlylimited and may be appropriately selected depending on, for example, theintended application/purpose of the light-emitting device. In general,the substrate is preferably a sheet. The substrate may have a single- ormulti-layered structure, and may be a single member or a combination oftwo or more members. The substrate may be opaque, colorless transparent,or colored transparent.

The substrate may be provided with a moisture permeation-preventinglayer (gas barrier layer) on the front or back surface thereof.

The moisture permeation-preventing layer (gas barrier layer) ispreferably made from an inorganic compound such as silicon nitride andsilicon oxide.

The moisture permeation-preventing layer (gas barrier layer) may beformed through, for example, high-frequency sputtering.

<Protective Layer>

The organic electroluminescence device of the present invention may beentirely protected with a protective layer.

The material contained in the protective layer may be any materials, solong as they have the function of preventing permeation of water,oxygen, etc., which promote degradation of the device. Examples thereofinclude metals such as In, Sn, Pb, Au, Cu, Ag, Al, Ti and Ni; metaloxides such as MgO, SiO, SiO₂, Al₂O₃, GeO, NiO, CaO, BaO, Fe₂O₃, Y₂O₃and TiO₂; metal nitrides such as SiN_(x) and SiN_(x)O_(y); metalfluorides such as MgF₂, LiF, AlF₃ and CaF₂; polyethylenes,polypropylenes, polymethyl methacrylates, polyimides, polyureas,polytetrafluoroethylenes, polychlorotrifluoroethylens,polydichlorofluoroethylenes, copolymers of chlorotrifluoroethylens anddichlorodifluoroethylenes, copolymers produced through compolymerizationof a monomer mixture containing tetrafluoroethylene and at least onecomonomer, fluorine-containing copolymers containing a ring structure inthe copolymerization main chain, water-absorbing materials each having awater absorption rate of 1% or more, and moisture permeation preventivesubstances each having a water absorption rate of 0.1% or less.

The method for forming the protective layer is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples thereof include a vacuum deposition method, a sputteringmethod, a reactive sputtering method, an MBE (molecular beam epitaxial)method, a cluster ion beam method, an ion plating method, a plasmapolymerization method (high-frequency excitation ion plating method), aplasma CVD method, a laser CVD method, a thermal CVD method, a gassource CVD method, a coating method, a printing method and a transfermethod.

<Seal Container>

The organic electroluminescence device of the present invention may beentirely sealed with a seal container. Moreover, a moisture absorber oran inert liquid may be incorporated into the space between the sealcontainer and the organic electroluminescence device.

The moisture absorber is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include barium oxide, sodium oxide, potassium oxide, calciumoxide, sodium sulfate, calcium sulfate, magnesium sulfate, phosphoruspentaoxide, calcium chloride, magnesium chloride, copper chloride,cesium fluoride, niobium fluoride, calcium bromide, vanadium bromide,molecular sieve, zeolite and magnesium oxide.

Also, the inert liquid is not particularly limited and may beappropriately selected depending on the intended purpose. Examplesthereof include paraffins; liquid paraffins; fluorine-based solventssuch as perfluoroalkanes, perfluoroamines and perfluoroethers;chlorinated solvents; and silicone oils.

<Resin Seal Layer>

The organic electroluminescence device of the present invention ispreferably sealed with a resin seal layer to prevent degradation of itsperformance due to oxygen or water contained in the air.

The resin material for the resin seal layer is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples thereof include acrylic resins, epoxy resins,fluorine-containing resins, silicone resins, rubber resins and esterresins. Among them, epoxy resins are preferred from the viewpoint ofpreventing water permeation. Among the epoxy resins, thermosetting epoxyresins and photo-curable epoxy resins are preferred.

The forming method for the resin seal layer is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples thereof include a method by coating a resin solution, a methodby press-bonding or hot press-bonding a resin sheet, and a method bypolymerizing under dry conditions (e.g., vapor deposition andsputtering).

<Sealing Adhesive>

The organic electroluminescence device may contain a sealing adhesivehaving the function of preventing permeation of moisture or oxygen fromthe edges thereof.

The material for the sealing adhesive may be those used in the resinseal layer. Among them, epoxy resins are preferred from the viewpoint ofpreventing water permeation. Among the epoxy resins, photo-curable epoxyadhesives and thermosetting epoxy adhesives are preferred.

Also, a filler is preferably added to the sealing adhesive. The filleris not particularly limited and may be appropriately selected dependingon the intended purpose. The filler is preferably inorganic materialssuch as SiO₂, SiO (silicon oxide), SiON (silicon oxynitride) and SiN(silicon nitride). The addition of the filler increases the viscosity ofthe sealing adhesive to improve production suitability and humidityresistance.

The sealing adhesive may also contain a desiccant. The desiccant is notparticularly limited and may be appropriately selected depending on theintended purpose. Examples thereof include barium oxide, calcium oxideor strontium oxide. The amount of the desiccant added to the sealingadhesive is preferably 0.01% by mass to 20% by mass, more preferably0.05% by mass to 15% by mass. When the amount is less than 0.01% bymass, the desiccant exhibits reduced effects. Whereas when the amount ismore than 20% by mass, it is difficult to homogeneously disperse thedesiccant in the sealing adhesive, which is not preferred.

In the present invention, the sealing adhesive containing the desiccantis applied in a predetermined amount using, for example, a dispenser.Thereafter, a second substrate is overlaid, followed by curing forsealing.

FIG. 5 is a schematic view of one exemplary layer structure of theorganic electroluminescence device of the present invention. An organicelectroluminescence device 10 has a layer structure in which a glasssubstrate 1 and an anode 2 (e.g., an ITO electrode), a hole injectionlayer 3, a hole transport layer 4, an emission layer 5, an electrontransport layer 6, an electron injection layer 7 (e.g., a lithiumfluoride-containing layer), a cathode 8 (e.g., an Al—Li electrode)disposed on the glass substrate in this order. Notably, the anode 2(e.g., the ITO electrode) and the cathode 8 (e.g., the Al—Li electrode)are connected together via a power source.

—Driving—

The organic electroluminescence device can emit light when a DC voltage(which, if necessary, contains AC components) (generally 2 volts to 15volts) or a DC is applied to between the anode and the cathode.

The organic electroluminescence device of the present invention can beapplied to an active matrix using a thin film transistor (TFT). Anactive layer of the thin film transistor may be made from, for example,amorphous silicon, high-temperature polysilicon, low-temperaturepolysilicon, microcrystalline silicon, oxide semiconductor, organicsemiconductor and carbon nanotube.

The thin film transistor used for the organic electroluminescence deviceof the present invention may be those described in, for example,International Publication No. WO2005/088726, JP-A No. 2006-165529 andU.S. Pat. Application Publication No. 2008/0237598 A1.

The organic electroluminescence device of the present invention is notparticularly limited. In the organic electroluminescence device, thelight-extraction efficiency can be further improved by various knownmethods. It is possible to increase the light-extraction efficiency toimprove the external quantum efficiency, for example, by processing thesurface shape of the substrate (for example, by forming a fineconcavo-convex pattern), by controlling the refractive index of thesubstrate, the ITO layer and/or the organic layer, or by controlling thethickness of the substrate, the ITO layer and/or the organic layer.

The manner in which light is extracted from the organicelectroluminescence device of the present invention may be top-emissionor bottom-emission.

The organic electroluminescence device may have a resonator structure.For example, on a transparent substrate are stacked a multi-layered filmmirror composed of a plurality of laminated films having differentrefractive indices, a transparent or semi-transparent electrode, anemission layer and a metal electrode. The light generated in theemission layer is repeatedly reflected between the multi-layered filmmirror and the metal electrode (which serve as reflection plates); i.e.,is resonated.

In another preferred embodiment, a transparent or semi-transparentelectrode and a metal electrode are stacked on a transparent substrate.In this structure, the light generated in the emission layer isrepeatedly reflected between the transparent or semi-transparentelectrode and the metal electrode (which serve as reflection plates);i.e., is resonated.

For forming the resonance structure, an optical path length determinedbased on the effective refractive index of two reflection plates, and onthe refractive index and the thickness of each of the layers between thereflection plates is adjusted to be an optimal value for obtaining adesired resonance wavelength. The calculation formula applied in thecase of the first embodiment is described in JP-A No. 09-180883. Thecalculation formula in the case of the second embodiment is described inJP-A No. 2004-127795.

—Application—

The application of the organic electroluminescence device of the presentinvention is not particularly limited and may be appropriately selecteddepending on the intended purpose. The organic electroluminescencedevice can be suitably used in, for example, display devices, displays,backlights, electrophotography, illuminating light sources, recordinglight sources, exposing light sources, reading light sources, markers,interior accessories and optical communication.

As a method for forming a full color-type display, there are known, forexample, as described in “Monthly Display,” September 2000, pp. 33 to37, a tricolor light emission method by arranging, on a substrate,organic electroluminescence devices corresponding to three primarycolors (blue color (B), green color (G) and red color (R)); a whitecolor method by separating white light emitted from an organicelectroluminescence device for white color emission into three primarycolors through a color filter; and a color conversion method byconverting a blue light emitted from an organic electroluminescencedevice for blue light emission into red color (R) and green color (G)through a fluorescent dye layer. Further, by combining a plurality oforganic electroluminescence devices emitting lights of different colorswhich are obtained by the above-described methods, plane-type lightsources emitting lights of desired colors can be obtained. For example,there are exemplified white light-emitting sources obtained by combiningblue and yellow light-emitting devices, and white light-emitting sourcesobtained by combining blue, green and red light-emitting devices.

(Method for Producing an Organic Electroluminescence Device)

A method for producing an organic electroluminescence device of thepresent invention includes at least a hole injection layer-forming step,a hole transport layer-forming step and an emission layer-forming step;and, if necessary, further includes appropriately selected other steps.

<Hole Injection Layer-Forming Step>

The hole injection layer-forming step is a step of forming the holeinjection layer.

The method for forming the hole injection layer is not particularlylimited and may be appropriately selected depending on the intendedpurpose. Examples thereof include dry film forming methods such as adeposition method and a sputtering method, wet coating methods (a slitcoating method and a spin coating method), transfer methods, printingmethods and inkjet methods.

Of these, wet coating methods are preferred from the viewpoints ofefficiently utilizing materials and covering irregularities in theelectrode surface.

<Hole Transport Layer-Forming Step>

The hole transport layer-forming step is a step of forming the holetransport layer.

The method for forming the hole transport layer is not particularlylimited and may be appropriately selected depending on the intendedpurpose. Examples thereof include dry film forming methods such as adeposition method and a sputtering method, wet coating methods (a slitcoating method and a spin coating method), transfer methods, printingmethods and inkjet methods.

Of these, wet coating methods are preferred from the viewpoint ofefficiently utilizing materials.

<Emission Layer-Forming Step>

The emission layer-forming step is a step of forming the emission layer.

The method for forming the emission layer is not particularly limitedand may be appropriately selected depending on the intended purpose.Examples thereof include dry film forming methods such as a depositionmethod and a sputtering method, wet coating methods (a slit coatingmethod and a spin coating method), transfer methods, printing methodsand inkjet methods.

Of these, wet coating methods are preferably employed, since theconcentration of the phosphorescent light-emitting material or the hostmaterial contained in the hole transport layer can be changed from aninterface between the hole transport layer and the emission layer to aninterface between the hole transport layer and the hole injection layer.

<Other Steps>

The other steps are not particularly limited and may be appropriatelyselected depending on the intended purpose. Examples thereof include anelectron transport layer-forming step, an electron injectionlayer-forming step, a hole blocking layer-forming step and an electronblocking layer-forming step.

EXAMPLES

The present invention will next be described by way of Examples, whichshould not be construed as limiting the present invention thereto.

Notably, in Examples and Comparative Examples, unless otherwisespecified, the deposition rate was 0.2 nm/sec. The deposition rate wasmeasured with a quartz crystal unit. Also, the layer thicknesses givenbelow were measured with a quartz crystal unit.

Example 1 —Production of Organic Electroluminescence Device—

A glass substrate (thickness: 0.7 mm, 25 mm×25 mm) was placed in awashing container. The substrate was washed in 2-propanol throughultrasonication, and then was UV-ozone treated for 30 min. The followinglayers were formed on this glass substrate.

First, ITO (Indium Tin Oxide) was deposited through sputtering on theglass substrate so as to form a 150 nm-thick anode. The obtainedtransparent supporting substrate was etched and washed.

Next, the anode (ITO) was coated through spin coating with a coatingliquid which had been prepared by dissolving or dispersing 14 parts bymass of arylamine derivative (trade name: PTPDES-2, product of CHEMIPROKASEI KAISHA, LTD., ionization potential (Ip)=5.45 eV) and 6 parts bymass of a compound having Structural Formula (2) serving as aphosphorescent light-emitting material (ionization potential (Ip)=5.34eV) in 980 parts by mass of cyclohexanone for electronics industry(product of KANTO KAGAKU). The resultant product was dried at 120° C.for 30 min and then annealed at 160° C. for 10 min, to thereby form ahole injection layer having a thickness of about 40 nm.

Next, the hole injection layer was coated through spin coating with acoating liquid which had been prepared by dissolving or dispersing 4parts by mass of a compound having Structural Formula (4) (arylaminederivative) (Mw=8,000) in 996 parts by mass of xylene for electronicsindustry (product of KANTO KAGAKU). The obtained product was dried at120° C. for 30 min and then annealed at 150° C. for 10 min, to therebyform a hole transport layer having a thickness of about 10 nm.

Notably, spin coating for the hole injection layer or the hole transportlayer was performed in a glove box (dew point: −68° C., oxygenconcentration: 10 ppm).

Next, the compound having Structural Formula (2), serving as thephosphorescent light-emitting material, and a compound having StructuralFormula (6), serving as the host material, were co-deposited at a ratioby mass of 10:90 on the hole transport layer by a vacuum depositionmethod, to thereby form an emission layer having a thickness of 40 nm.

Next, BAlq(bis-(2-methyl-8-quinolinolato)-4-(phenyl-phenolate)-aluminum-(III)) wasdeposited on the emission layer by a vacuum deposition method, tothereby form an electron transport layer having a thickness of 40 nm.

Next, lithium fluoride (LiF) was deposited on the electron transportlayer to form an electron injection layer having a thickness of 1 nm.

Next, metal aluminum was deposited on the electron injection layer toform a cathode having a thickness of 70 nm.

The thus-obtained laminate was placed in a glove box which had beenpurged with argon gas, and then was sealed in a stainless steel sealingcan using a UV-ray curable adhesive (XNR5516HV, product of Nagase-CIBALtd.).

The synthesis schemes of the compounds having Structural Formulas (2),(4) and (6) are as follows.

<Synthesis Scheme of the Compound Having Structural Formula (2)>

<Synthesis Scheme of the Compound Having Structural Formula (4)>

<Synthesis Scheme of the Compound Having Structural Formula (6)>

Example 2

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole transport layer was formed using acoating liquid which had been prepared by dissolving or dispersing 10.4parts by mass of the compound having Structural Formula (4) (as thearylamine derivative) (Mw=8,000), 0.26 parts by mass of the compoundhaving Structural Formula (2) (as the phosphorescent light-emittingmaterial) and 2.34 parts by mass of the compound having StructuralFormula (6) (as the host material) in 987 parts by mass of xylene forelectronics industry (product of KANTO KAGAKU).

Example 3

An organic electroluminescence device was produced in the same manner asin Example 2, except that an emission layer (thickness: 35 nm) wasformed in a glove box through spin coating of an emission layer-coatingliquid, followed by drying at 100° C. for 30 min. Here, the emissionlayer-coating liquid was formed as follows. Specifically, 1 part by massof the compound having Structural Formula (2) (as the phosphorescentlight-emitting material) and 9 parts by mass of the compound havingStructural Formula (6) (as the host material) were dissolved ordispersed in 990 parts by mass of 2-butanone for electronics industry(product of KANTO KAGAKU). Then, molecular sieve (trade name: molecularsieve 5A 1/16, product of Wako Pure Chemical Industries, Ltd.) was addedto the resultant mixture, followed by filtration with a syringe filter(pore size: 0.22 μm) in the glove box.

Through X-ray photoelectron spectroscopy of the laminate including thehole transport layer and the emission layer formed thereon by coating,the concentration of the Ir complex was found to be gradually decreasedin the hole transport layer from an interface between the hole transportlayer and the emission layer to an interface between the hole transportlayer and the hole injection layer (FIG. 6).

Example 4

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole transport layer was formed using acoating liquid which had been prepared by dissolving or dispersing 12.74parts by mass of the compound having Structural Formula (4) (Mw=8,000)(as the arylamine derivative) and 0.26 parts by mass of the compoundhaving Structural Formula (2) (as the phosphorescent light-emittingmaterial) in 987 parts by mass of xylene for electronics industry(product of KANTO KAGAKU).

Example 5

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole injection layer was formed throughspin coating of a coating liquid which had been prepared by dissolvingor dispersing 11 parts by mass of PTPDES-2 (as the arylamine derivative)and 9 parts by mass of the compound having Structural Formula (2) (asthe phosphorescent light-emitting material) in 980 parts by mass ofcyclohexane for electronics industry (product of KANTO KAGAKU) and thehole transport layer was formed using a coating liquid which had beenprepared by dissolving or dispersing 12.61 parts by mass of the compoundhaving Structural Formula (4) (as the arylamine derivative) and 0.39parts by mass of the compound having Structural Formula (2) (as thephosphorescent light-emitting material) in 987 parts by mass of xylenefor electronics industry (product of KANTO KAGAKU).

Example 6

An organic electroluminescence device was produced in the same manner asin Example 2, except that the compound having the following StructuralFormula (1) (trade name: Ir(ppy)₃, product of CHEMIPRO KASEI KAISHA,LTD.) (the phosphorescent light-emitting material) was used for theformation of the hole injection layer and the hole transport layer.

Example 7

An organic electroluminescence device was produced in the same manner asin Example 2, except that Firpic (iridium(III)bis(4,6-difluorophenylpyridinato)picolate) (product of CHEMIPRO KASEIKAISHA, LTD, ionization potential (Ip)=5.8 eV) (the phosphorescentlight-emitting material) was used for the formation of the holeinjection layer and the hole transport layer.

Comparative Example 1

An organic electroluminescence device was produced in the same manner asin Example 1, except that no phosphorescent light-emitting material wasadded to the coating liquid used for the formation of the hole injectionlayer.

Comparative Example 2

An organic electroluminescence device was produced in the same manner asin Example 2, except that no phosphorescent light-emitting material wasadded to the coating liquid used for the formation of the hole injectionlayer.

Comparative Example 3

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole injection layer was formed using acoating liquid which had been prepared by dissolving or dispersing 4parts by mass of PTPDES-2 (as the arylamine derivative) and 16 parts bymass of the compound having Structural Formula (2) (as thephosphorescent light-emitting material) in 980 parts by mass ofcyclohexanone for electronics industry (product of KANTO KAGAKU).

Comparative Example 4

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole injection layer was formed using acoating liquid which had been prepared by dissolving or dispersing 9parts by mass of PTPDES-2 (as the arylamine derivative) and 11 parts bymass of the compound having Structural Formula (2) (as thephosphorescent light-emitting material) in 980 parts by mass of xylenefor electronics industry (product of KANTO KAGAKU).

Example 8

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole injection layer was formed using acoating liquid which had been prepared by dissolving or dispersing 17.8parts by mass of PTPDES-2 (as the arylamine derivative) and 2.2 parts bymass of the compound having Structural Formula (2) (as thephosphorescent light-emitting material) in 980 parts by mass ofcyclohexane for electronics industry (product of KANTO KAGAKU).

Example 9

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole injection layer was formed using acoating liquid which had been prepared by dissolving or dispersing 7.2parts by mass of PTPDES-2 (as the arylamine derivative), 3 parts by massof S-320 (crosslinking agent, product of AZmax. co) and 9.8 parts bymass of the compound having Structural Formula (2) (as thephosphorescent light-emitting material) in 980 parts by mass ofcyclohexane for electronics industry (product of KANTO KAGAKU) and bystirring the resultant mixture for 1 hour.

Example 10

An organic electroluminescence device was produced in the same manner asin Example 1, except that an emission layer (thickness: 40 nm) wasformed by co-depositing the compound having Structural Formula (2) (asthe phosphorescent light-emitting material) and the compound havingStructural Formula (6) (as the host material) at a ratio by mass of 5:95by a vacuum deposition method.

Example 11

A hole injection layer was formed in the same manner as in Example 1,except that the arylamine derivative was changed to PTPDES (trade name)(product of CHEMIPRO KASEI KAISHA, LTD., ionization potential (Ip=5.43eV) (14 parts by mass) and that the phosphorescent light-emittingmaterial was changed to a compound having Structural Formula (7)(Compound 11 described in U.S. Pat. WO2009/073245) (6 parts by mass).

Next, 10 parts by mass of a compound having the following StructuralFormula (8) (HTL-1 described in U.S. Pat. No. 2008/0220265) serving as ahole transporting material was dissolved in 990 parts by mass of toluene(dehydrated) (product of Wako Pure Chemical Industries, Ltd.), tothereby prepare a hole transport layer-coating liquid. The holeinjection layer was coated through spin coating with the hole transportlayer-coating liquid, followed by drying at 200° C. for 30 min, tothereby form a hole transport layer having a thickness of 10 nm.

Then, an organic electroluminescence device was produced in the samemanner as in Example 1, except that an emission layer (thickness: 30 nm)was formed on the above-formed hole transport layer by co-depositing thecompound having Structural Formula (7) (as the phosphorescentlight-emitting material) and a compound having Structural Formula (9)(as the host material) at a ratio by mass of 15:85.

Example 12

An organic electroluminescence device was produced in the same manner asin Example 11, except that the compound having Structural Formula (8)(as the hole transporting material) and the compound having StructuralFormula (7) (as the phosphorescent light-emitting material) weredissolved in toluene at a ratio by mass of 95:5.

Example 13

An organic electroluminescence device was produced in the same manner asin Example 11, except that the host material of the emission layer waschanged to a compound having Structural Formula (10).

Comparative Example 5

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole injection layer was formed using acoating liquid which had been prepared by dissolving or dispersing 18.2parts by mass of PTPDES-2 (as the arylamine derivative) and 1.8 parts bymass of the compound having Structural Formula (2) (as thephosphorescent light-emitting material) in 980 parts by mass ofcyclohexanone for electronics industry (product of KANTO KAGAKU).

Comparative Example 6

An organic electroluminescence device was produced in the same mannersas in Example 1, except that the hole injection layer was formed using acoating liquid which had been prepared by dissolving or dispersing 10parts by mass of PTPDES-2 (as the arylamine derivative) and 10 parts bymass of the compound having Structural Formula (2) (as thephosphorescent light-emitting material) in 980 parts by mass ofcyclohexanone for electronics industry (product of KANTO KAGAKU).

Comparative Example 7

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole transport layer was formed using acoating liquid which had been prepared by dissolving or dispersing 10.4parts by mass of the compound having Structural Formula (4) (Mw=8,000)(as the arylamine derivative) and 2.6 parts by mass of the compoundhaving Structural Formula (2) (as the phosphorescent light-emittingmaterial) in 987 parts by mass of xylene for electronics industry(product of KANTO KAGAKU).

Comparative Example 8

An organic electroluminescence device was produced in the same manner asin Example 1, except that the hole transport layer was formed using acoating liquid which had been prepared by dissolving or dispersing 8.06parts by mass of the compound having Structural Formula (4) (Mw=8,000)(as the arylamine derivative), 2.6 parts by mass of the compound havingStructural Formula (2) (as the phosphorescent light-emitting material)and 2.34 parts by mass of the compound having Structural Formula (6) (asthe host material) in 987 parts by mass of xylene for electronicsindustry (product of KANTO KAGAKU).

Comparative Example 9

An organic electroluminescence device was produced in the same manner asin Example 11, except that the hole injection layer was formed from onlyPTPDES.

(Evaluation)

Each of the phosphorescent light-emitting materials used in Examples 1to 13 and Comparative Examples 1 to 9 were measured for saturationsolubility and thermodecomposition temperature as follows.

<Measurement of Saturation Solubility>

Using cyclohexanone as a solvent, saturation solutions of thephosphorescent light-emitting materials (Ir complexes) used in Examples1 to 13 and Comparative Examples 1 to 9 were prepared. Separately,solutions having different concentrations for obtaining a calibrationcurve (0.05 wt % and 0.1 wt %) were prepared. Each solution was measuredfor absorbance with a spectrophotometer (product of ShimadzuCorporation, trade name “UV-3600”). The saturation solubility of each Ircomplex was measured on the basis of the ratio between the obtainedabsorbances. The results are shown in Table 1.

<Measurement of Thermodecomposition Temperature>

Using a thermogravimetry differential thermal analyzer (product of SITNano Technology Inc., trade name “EXSTAR TG/DTA6000”), each of the Ircomplex-saturation solutions was heated to 500° C. at a temperatureincreasing rate of 10° C./min in a nitrogen atmosphere for measuring achange in weight. The temperature at which the weight was changed by 1%was defined as the thermodecomposition temperature. The results areshown in Table 1.

TABLE 1 Saturation solubility Thermodecomposition (wt %) Temperature (°C.) Structural Formula (1) 0.07 355 Firpic 1.8 327 Structural Formula(2) 2.9 276 Structural Formula (7) >4 320

As is clear from Table 1, the Ir complexes having different ligands werefound to exhibit high solubility. In particular, the complex havingStructural Formula (7), whose ligands are coordinated via only C and N,was found to exhibit remarkably high solubility. In addition, thecomplex having Structural Formula (7) was found to have athermodecomposition temperature higher than that of the complex havingStructural Formula (2) which is an acac complex having high solubility,and thus to have excellent stability.

Next, each of the above-produced organic electroluminescence devices ofExamples 1 to 13 and Comparative Examples 1 to 9 as shown in Table 2 wasmeasured as follows for external quantum efficiency and Turn On voltage(a voltage at which each organic electroluminescence device begins toemit light).

Notably, the concentration of the phosphorescent light-emitting materialin each layer of the organic electroluminescence device of Example 3 wasmeasured based on the Ir concentration profile obtained throughsecondary ion mass spectrometry. Also, the host material was consideredas permeating underlying layers similar to the phosphorescentlight-emitting material.

<Measurement of External Quantum Efficiency>

Using source measure unit 2400 (product of TOYO Corporation), DC voltagewas applied to each device for light emission. The emission spectrum andbrightness were measured with spectrum analyzer SR-3 (product of TOPCONCORPORATION). On the basis of the obtained values, the external quantumefficiency at 10 mA/cm² (current) was calculated by a brightnessconversion method. The results are shown in Tables 3-1 and 3-2.

Notably, in Tables 3-1, 3-2 and 4, the external quantum efficiency inComparative Example 1 was used as a reference. The external quantumefficiencies in the other Examples and Comparative Examples wereexpressed as relative values to the external quantum efficiency inComparative Example 1 (i.e., which was regarded as 1).

Furthermore, in the column “Lamination coating” in Table 3-2,“Performable” means that the hole transport layer could be formed on thehole injection layer through coating, and “Not performable” means thatthe hole transport layer could not be formed on the hole injection layerthrough coating. Table 4 shows actual measurement values of externalquantum efficiency in Examples 11 to 13 and Comparative Example 9.

<Measurement of Turn on Voltage>

Using source meter 2400 (product of Keithley Instruments Inc.), thevoltage at 0.025 mA/cm² (current density) was measured.

<Evaluation of Turn on Voltage>

On the basis of the Turn On voltage in Comparative Example 1(reference), the Turn On voltages in the other Examples and ComparativeExamples were expressed as “Lower than reference,” “Equal to reference”or “Higher than reference.” The results are shown in Tables 3-1, 3-2 and4.

TABLE 2 Hole injection layer Hole transport layer Emission layerPhosphorescent Phosphorescent Hole transport layer Phosphorescentlight-emitting Hole injection layer light-emitting Hole transport layerHole transport light-emitting Emission layer material Host materialmaterial Host material material material Host material Ex. 1 S.F. (2) —— — S.F. (4) S.F. (2) S.F. (6) Ex. 2 S.F. (2) — S.F. (2) S.F. (6) S.F.(4) S.F. (2) S.F. (6) Ex. 3 S.F. (2) — S.F. (2) S.F. (6) S.F. (4) S.F.(2) S.F. (6) Ex. 4 S.F. (2) — S.F. (2) — S.F. (4) S.F. (2) S.F. (6) Ex.5 S.F. (2) — S.F. (2) — S.F. (4) S.F. (2) S.F. (6) Ex. 6 S.F. (1) — S.F.(1) S.F. (6) S.F. (4) S.F. (2) S.F. (6) Ex. 7 Firpic — Firpic S.F. (6)S.F. (4) S.F. (2) S.F. (6) Ex. 8 S.F. (2) — — — S.F. (4) S.F. (2) S.F.(6) Ex. 9 S.F. (2) — — — S.F. (4) S.F. (2) S.F. (6) Ex. 10 S.F. (2) — —— S.F. (4) S.F. (2) S.F. (6) Ex. 11 S.F. (7) — — — S.F. (8) S.F. (7)S.F. (9) Ex. 12 S.F. (7) — S.F. (7) — S.F. (8) S.F. (7) S.F. (9) Ex. 13S.F. (7) — — — S.F. (8) S.F. (7) S.F. (10) Comp. — — — — S.F. (4) S.F.(2) S.F. (6) Ex. 1 Comp. — — S.F. (2) S.F. (6) S.F. (4) S.F. (2) S.F.(6) Ex. 2 Comp. S.F. (2) — — — S.F. (4) S.F. (2) S.F. (6) Ex. 3 Comp.S.F. (2) — — — S.F. (4) S.F. (2) S.F. (6) Ex. 4 Comp. S.F. (2) — — —S.F. (4) S.F. (2) S.F. (6) Ex. 5 Comp. S.F. (2) — — — S.F. (4) S.F. (2)S.F. (6) Ex. 6 Comp. S.F. (2) — S.F. (2) — S.F. (4) S.F. (2) S.F. (6)Ex. 7 Comp. S.F. (2) — S.F. (2) S.F. (6) S.F. (4) S.F. (2) S.F. (6) Ex.8 Comp. — — — — S.F. (8) S.F. (7) S.F. (9) Ex. 9 Note: “S.F.” is anabbreviation of Structural Formula.

TABLE 3-1 Hole injection layer Hole injection layer Hole transport layerHole transport layer Emission layer Emission layer Conc. ofphosphorescent Conc. of host Conc. of phosphorescent Conc. of host Conc.of phosphorescent Conc. of host light-emitting material materiallight-emitting material material light-emitting material material (% bymass) (% by mass) (% by mass) (% by mass) (% by mass) (% by mass) Ex. 130 0 0 0 10 90 Ex. 2 30 0 2 18 10 90 Ex. 3 30 0 Phosphorescentlight-emitting 10 90 material and host material were diffused fromemission layer and each had a concentration gradient Ex. 4 30 0 2 0 1090 Ex. 5 45 0 3 0 10 90 Ex. 6 30 0 2 18 10 90 Ex. 7 30 0 2 18 10 90 Ex.8 11 0 0 0 10 90 Ex. 9 49 0 0 0 10 90 Ex. 10 30 0 0 0 5 95 Ex. 11 30 0 00 15 85 Ex. 12 30 0 5 0 15 85 Ex. 13 30 0 0 0 15 85 Comp. 0 0 0 0 10 90Ex. 1 Comp. 0 0 2 18 10 90 Ex. 2 Comp. 80 0 0 0 10 90 Ex. 3 Comp. 55 0 00 10 90 Ex. 4 Comp. 9 0 0 0 10 90 Ex. 5 Comp. 50 0 0 0 10 90 Ex. 6 Comp.30 0 20 0 10 90 Ex. 7 Comp. 30 0 20 18 10 90 Ex. 8 Comp. 0 0 0 0 15 85Ex. 9

TABLE 3-2 Relative external quantum Lamination efficiency Turn Onvoltage coating Remarks Ex. 1 1.4 Lower than ref. Performable — Ex. 21.7 Lower than ref. Performable — Ex. 3 1.8 Lower than ref. PerformableEmission layer was formed through coating Ex. 4 1.5 Lower than ref.Performable — Ex. 5 1.7 Lower than ref. Performable — Ex. 6 1.3 Lowerthan ref. Performable Phosphorescent light-emitting material: Ir(ppy)₃(Ip = 5.45 eV) Dark spots existed Ex. 7 1.3 Lower than ref. PerformablePhosphorescent light-emitting material: Firpic (Ip = 5.8 eV) Lowdurability Ex. 8 1.3 Lower than ref. Performable — Ex. 9 1.4 Lower thanref. Performable — Ex. 10 1.3 Lower than ref. Performable — Ex. 11 — —Performable — Ex. 12 — — Performable — Ex. 13 — — Performable — Comp.1.0 Reference (ref.) Performable — Ex. 1 Comp. 1.2 Equal to ref.Performable — Ex. 2 Comp. Not evaluated Not evaluated Not performableHole injection layer dissolved Ex. 3 Comp. Not evaluated Not evaluatedNot performable Hole injection layer dissolved Ex. 4 Comp. 1.0 Equal toref. Performable Not effective Ex. 5 Comp. 0.9 Lower than ref.Performable Electron transport layer emitted light Ex. 6 Comp. 0.9 Lowerthan ref. Performable Electron transport layer emitted light Ex. 7 Comp.0.9 Lower than ref. Performable Electron transport layer emitted lightEx. 8 Comp. — — Performable — Ex. 9

TABLE 4 External quantum efficiency (%) Turn On voltage (V) Ex. 11 4.08.2 Ex. 12 4.7 8.2 Ex. 13 5.2 7.5 Comp. Ex. 9 3.9 8.4

From Tables 3-1 and 3-2, the organic electroluminescence devices ofComparative Examples 1 to 9 were found to be higher in external quantumefficiency than those of Examples 1 to 13 in which the amount of thephosphorescent light-emitting material contained in the hole injectionlayer was 10% by mass or more but less than 50% by mass, theconcentration of the phosphorescent light-emitting material contained inthe hole transport layer was lower than that in the hole injectionlayer, and the concentration of the phosphorescent light-emittingmaterial contained in the emission layer was lower than that in the holeinjection layer and higher than that in the hole transport layer.

Also, from Tables 3-1 and 3-2, the hole transport layer was found tohave concentration gradients of the phosphorescent light-emittingmaterial and the host material in the organic electroluminescence deviceof Example 3 whose emission layer was formed through coating.

Furthermore, from Tables 3-1 and 3-2, when the concentration of thephosphorescent light-emitting material contained in the hole injectionlayer was higher than 50%, the hole transport layer could not be formedthereon through coating (i.e., lamination coating was not performable)since the hole injection layer dissolved in the coating liquid used forthe formation of the hole transport layer.

Moreover, use of the compound having Structural Formula (1) as thephosphorescent light-emitting material was found to generate dark spotsas a result of aggregation, since this compound has low dissolvabilityto a solvent used for coating. Here, the “dark spots” are regions wherelight is emitted.

Also, the organic electroluminescence device containing Firpic as thephosphorescent light-emitting material was found to be low indurability. Notably, durability was evaluated by measuring the timerequired that the initial brightness (1,000 cd/m²) was decreased by halfduring driving at a constant current.

Moreover, from Table 4, when the phosphorescent light-emitting materialwas incorporated into the hole injection layer, the external quantumefficiency was found to be improved and the Turn On voltage was found todecrease. In particular, when the phosphorescent light-emitting materialwas also incorporated into the hole transport layer, more improvedperformances were found to be obtained. In addition, use of the hosthaving a nitrile group was found to provide more improved performances.

INDUSTRIAL APPLICABILITY

The organic electroluminescence devices of the present invention canattain excellent light-emission efficiency and long light-emission time,and thus, can be suitably used in, for example, display devices,displays, backlights, electrophotography, illuminating light sources,recording light sources, exposing light sources, reading light sources,markers, interior accessories and optical communication.

REFERENCE SINGS LIST

-   -   1 Substrate    -   2 Anode    -   3 Hole injection layer    -   4 Hole transport layer    -   5 Emission layer    -   6 Electron transport layer    -   7 Electron injection layer    -   8 Cathode    -   10 Organic electroluminescence device

1. An organic electroluminescence device comprising: an anode, acathode, an organic layer disposed between the anode and the cathode,the organic layer containing a hole injection layer, a hole transportlayer and an emission layer containing a host material, wherein the holeinjection layer, the hole transport layer and the emission layer eachcontain a phosphorescent light-emitting material, wherein the holeinjection layer contains the phosphorescent light-emitting material inan amount of 10% by mass or more but less than 50% by mass, and whereina concentration of the phosphorescent light-emitting material containedin the hole transport layer is lower than that in the hole injectionlayer, and a concentration of the phosphorescent light-emitting materialcontained in the emission layer is lower than that in the hole injectionlayer and higher than that in the hole transport layer.
 2. The organicelectroluminescence device according to claim 1, wherein the holetransport layer further contains the host material.
 3. The organicelectroluminescence device according to claim 2, wherein a ratio by massof the phosphorescent light-emitting material to the host material inthe emission layer is one to ten times a ratio by mass of thephosphorescent light-emitting material to the host material in the holetransport layer.
 4. The organic electroluminescence device according toclaim 1, wherein the concentration of the phosphorescent light-emittingmaterial contained in the hole transport layer is changed from aninterface between the hole transport layer and the emission layer to aninterface between the hole transport layer and the hole injection layer.5. The organic electroluminescence device according to claim 2, whereinthe concentration of the host material contained in the hole transportlayer is changed from an interface between the hole transport layer andthe emission layer to an interface between the hole transport layer andthe hole injection layer.
 6. The organic electroluminescence deviceaccording to claim 1, wherein the phosphorescent light-emitting materialhas an asymmetric structure.
 7. The organic electroluminescence deviceaccording to claim 1, wherein the phosphorescent light-emitting materialis a compound represented by General Formula (1) below:(L1)₂-Ir-(L2)₁  General Formula (1) where L1 denotes a ligand and L2denotes a ligand different from L1.
 8. The organic electroluminescencedevice according to claim 1, wherein the host material is a compoundrepresented by General Formula (2) below:

where R represents a t-butyl group, a t-amyl group, a trimethylsilylgroup, a triphenylsilyl group or a phenyl group, and R₁ to R₂₃ eachrepresent a hydrogen atom, a C1-C5 alkyl group, a cyano group, afluorine atom, a trifluoro group, a trimethylsilyl group, atriphenylsilyl group or a phenyl group.
 9. The organicelectroluminescence device according to claim 1, wherein the holeinjection layer further contains an arylamine derivative and anionization potential of the arylamine derivative is 4.8 eV to 5.8 eV andwherein a difference between the ionization potential of the arylaminederivative and an ionization potential of the phosphorescentlight-emitting material contained in the hole injection layer is within±0.2 eV.
 10. An organic electroluminescence device-producing method forproducing the organic electroluminescence device according to claim 1,comprising: forming the hole injection layer, the hole transport layerand the emission layer through coating.
 11. The organicelectroluminescence device-producing method according to claim 10,wherein the phosphorescent light-emitting material is soluble to asolvent used for the coating.